Voltages and current transients are major causes of integrated circuit failure in electronic systems. Transients are generated from a variety of sources both internal and external to the system. For instance, common sources of transients include normal switching operations of power supplies, AC line fluctuations, lightning surges, and electrostatic discharge (ESD).
Transient voltage suppressors (TVS) are commonly employed for protecting integrated circuits from damages due to the occurrences of transients or over-voltage conditions at the integrated circuit. Over-voltage protection are important for consumer devices or the Internet of Things devices as these electronic devices are exposed to frequent human handling and, as a result, may be susceptible to ESD or transient voltage events that may damage the devices.
In particular, the power supply pins and the data pins of the electronic devices both require protection from over-voltages conditions due to ESD events or switching and lightning transient events. Typically, the power supply pins need high surge protection but can tolerate protection devices with higher capacitance. Meanwhile, the data pins, which may operate at high data speed, requires protection devices that provide surge protection with low capacitance so as not to interfere with the data speed of the protected data pins.
Existing TVS protection solution applied to input/output (I/O) terminals in high speed applications exist both in vertical and lateral type of semiconductor circuit structures. In conventional vertical unidirectional structures, the I/O current during ESD flows from high side and low side steering diode vertically to ground. However, when these vertical structures are used for bidirectional TVS, the I/O current flows vertically and then laterally to ground via the second I/O terminal. Due to the lateral current flow, the parasitic resistance between vertical and lateral current flow path increases which degrades the clamping voltage.